Does a bathroom need an extractor fan?
New or renovated bathrooms need extraction to Building Regulations Part F — 15 litres per second intermittent, ducted to outside air. An openable window alone satisfies the letter for some existing rooms, but in practice every south London bathroom we refit gets a proper ducted fan: it is the single biggest mould preventer there is.
The regulation sets the number — 15 l/s for a bathroom — but the detail that decides whether a fan works is the ducting. A fan venting into the loft or a ceiling void just relocates the moisture into the building's structure, where it condenses and rots; we duct to an external wall or roof terminal, full stop. The number of 'broken' extractors we replace that turn out to be fine fans venting nowhere is remarkable.
South London's converted flats are the repeat offenders: internal bathrooms created in the 1980s with a flexible hose disappearing into a shared void. Renovating those rooms, the extraction route is part of the design — a rigid duct run to the rear elevation, sized so the fan's rated flow survives the duct length.
Spec-wise: continuous-running dMEV fans have overtaken pull-cord intermittents for wet rooms that get heavy use — near-silent trickle extraction with humidity boost, no one ever 'forgets to run it'. In new-build flats with MVHR whole-dwelling systems (Greenwich Peninsula, central Croydon towers), the bathroom must connect into the MVHR correctly rather than gaining a hole-in-wall fan that unbalances the system — a detail builder-grade refits routinely get wrong.
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